Pickling of aluminum



Feb- 13, 1951 E. R. zADEMAcH Erm. 2,541,901

PICKLING OF ALUMINUM Filed Oct. 26, 1944 y Patented Feb. 13, 1951 PICKLING F ALUMINUM Erich R. Zademach, Hillside, and William W. Clarke, Summit, N. J., assignors to Metalwash Machinery Company, Irvington, N. J a copartnership Application October 26, 1944, Serial No. 560,490

This invention relates to a novel method of pickling aluminum and its alloys. Aluminum sheet, when rolled, becomes work hardened and roughened upon the surface; and it may also become oxidized and have small particles of dirt or other foreign material rolled into the surface. In order to obtain a bright or so-called mirror finish, as for sheets intended for use in reiiectors, it is necessary to remove this surface prior to the iinish ro'ling of the material.

It is customary, moreover, to etch the surface of rods, bars, castings, forgings and extrusions to remove the surface layer and thus reveal any ssure or other flaws which may have been produced during the washing of the parts and which would otherwise be concealed by the deoxidized surface of the metal.

This has been done in the past by dipping the 1 Claim. (Cl. 134-3) aluminum sheets, bars, rods, etc. in a tank containing a 5 to 20% caustic solution at temperatures ranging from 160 .to 210 degrees F.. and allowing them to remain there for from 5 to 20 minutes. This dissolves from .001" to .008" of the surface and leaves the parts covered with a thick, black slime of sodium aluminate,

The parts are then rinsed in a tank of water and immersed in a tank of cold nitric acid ranging anywhere from to 50% in strength. The nitric acid dip removes the sodium aluminate and leaves the metal in a bright condition with a matte or etched surface, after which the parts are rinsed in a tank of warm water and allowed to dry from their own heat.

This treatment has not been completely satisfactory, particularly in the treatment of sheet material, as any water remaining on the sheet produced a stain, which stain is elongated in the subsequent rolling and mars the otherwise mirror finish of the piece.

In the present invention the caustic, the rinses and the nitric acid are sprayed on the aluminum. This produces a very uniform removal of the aluminum. Moreover, the force of the sprays prevents the formation .of a sodium aluminate coating on the sheet, thus exposing the surface of the metal continuously to the action of the solution, thus shortening the time required for the removal of a given' thickness of metal by a very substantial margin and making it possible, moreover, to use a much lower concentration of nitric acid, thus reducing the consumption thereof. After the'flnal water spray the aluminum sheet is subjected to cold and hot blasts of air, in succession, and thereupon emerges from the machine in a dry stain-free condition.

mately 160 to 200.

One object of the invention is to provide an improved method of pickling aluminum.

Another object of the invention is to provide an improved method of treatment of aluminum sheet.

Another object of the invention is to provide a method for pickling aluminum by which the nitric acid consumption will be reduced, and the time of operation will be substantially diminished.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specication and' an inspection of the accompanying drawings in which:

Figure l `is a schematic plan view of our im proved machine; and

Figure 2 is a schematic sectional elevation taken on the line 2-2 of the machine of Figure 1.

Figure 3 is a longitudinal section through the I2 on a track II through a, casing generally indicated at I0. Appropriate sprays I4 are located at both sides of the path of the material so that all surfaces of the material are uniformly treated. The aluminum rst enters thecompartment A where it is sprayed with a 10% solution of sodium hydroxide at a pressure at an average of about 20 to 25 pounds and a temperature of approxi- 'Ihis treatment removes approximately .001 inch per minute of the surface of the aluminum. The removal is almost as precise as a machine operation and, in addition, the

lforce of the sprays removes the sodium aluminate which is formed. From the compartment A the aluminum passes along the track into the compartments B and B' where it is sprayed with water to remove the caustic solution. The rst washing is done in compartment B and since this is the first rinse and accomplishes the preliminary removal of the sodium aluminate, this water is then discharged. The water in the rinse tank B is recirculated. The sheet then passes to the compartment C where it is sprayed with nitric acid in a concentration of between 10% and 15% at a temperature of about F. Then the sheet passes to compartments D and D' where it is given the nal cold water spray. The rinse section D is supplied with cold water recirculated by the pump F from the tank E, and a portion of this water is transmitted to the rinse section B to supply a, suicient quantity of water in that section. The rinse section D is supplied with fresh water from the supply line indicated, so that when the aluminum emerges it has been rinsed with fresh water. The water from the section D returns to the tank E and thereafter it is recirculated through the rinse section D.

The supply of water to section Dv can be regulated to equal approximately the quantity 'discharged into the sewer from section B. After the sheet emerges from the compartment D', the sheet passes into the dryers. The rst dryer I is a cold blast dryer where the air preferably at a pressure of 11/2 lbs. is blown into the sheet from the nozzle pipes 48 indicated in Figure 3. This air is supplied by the turbo-blower 45 and the pipes 48 are preferably located diagonally to the sheet so that they blow drops of water back and down rather than spreading the drops. The sheet then passes into the hot blast dryer J which is supplied with air by the turbo blower 46 and the heater 41 which removes the remaining water.

Due to the fact that the sodium hydroxide spray removes most of the sludge formed, the nitric acid spray is not required to be long continued and it does not require a high percentage of acid, thereby considerably decreasing the quantity of acid used as compared to the previous tank method.

A certain amount of sodium aluminate sludge accumulates in the caustic solution, and this sludge is removed and the caustic solution recovered as described in our concurrently led application Serial No, 560,491, led October 26, 1944, now abandoned.

We have described what we lbelieve to be the best embodiments of our invention. We do not wish, however, to be conned to the embodiments described, but what we desire to cover by Letters Patent is set forth in the appended claim.

We claim:

The method of pickling aluminum including the steps of spraying the aluminum with sodium hydroxide solution at a pressure suillcient to cause the reaction layer of sodium aluminate to be mechanically removed by said spray, treating said aluminum in succession with a rinsing water spray, a nitric acid spray, water spray and then with a cold air blast in a direction to mechanically remove substantially all the water on said aluminum followed by a hot air blast to prevent vapor condensation on said aluminum.

ERICH R. ZADEMACH. WILLIAM W. CLARKE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,355,074 Cleveland Oct. 5, 1920 1,421,055 Adams June 27, 1922 1,445,775 Lathrop Feb. 20, 1923 1,572,848 Porter Feb, 9, 1926 1,705,944 Siegmund Mar. 19, 1929 1,891,549 Lane Dec. 20, 1932 2,137,988 Hempel Nov. 22, 1938 2,235,978 Braucher Mar. 25, 1941 2,347,742 Keene May 2, 1944 2,359,088 Croft Sept, 26, 1944 

